1. Place the potatoes and the onion in a pot and add enough salted water to cover by at least 3 inches. Bring the water to a boil and immediately reduce to a simmer. Cook until the potatoes are tender, about 15 minutes.
2. Meanwhile, make the dressing by combining the balsamic vinegar, cider vinegar, Dijon mustard, and honey in a small mixing bowl. Whisk to combine. Slowly drizzle in the olive oil in a slow, steady stream, stirring constantly. Stir in the shallots, chervil, chives, parsley, ½ teaspoon of the salt, and ¼ teaspoon of the pepper. Let the dressing sit for at least 10 minutes at room temperature for the herbs to infuse their flavor.
3. Drain the potatoes and discard the onion. Transfer the potatoes to a serving bowl. Stir the dressing just before pouring it over the potatoes, season with the remaining salt and pepper, and toss to coat well. Serve warm or at room temperature.